I think it is C. I hope I helped.
Answer: A thin membrane.
Explanation:
When a sound signal is allowed to pass through the voice coil suspended between permanent magnet, magnetic field will be induced which will cause vibration in the diaphragm - a thin membrane causing disturbance of air in the surrounding of membranes which eventually produce sound waves.
Therefore, we can conclude that a thin membrane of the loud speaker produces sound waves
D = 1/f, where D is the power in diopters and f is the focal length in meters.
D=1/20
<u>D=0.05</u>
The period is the time taken by the wave to complete an oscillation. The frequency of the given sound is 500 Hz.
<h2>
Period:</h2>
It is the time taken by the wave to complete an oscillation. The frequency is inversely proportional to the time:

Where,
- frequency
- period = 0.002 s
Put the value in the equation,

Therefore, the frequency of the given sound is 500 Hz.
Learn more about Period:
brainly.com/question/842349
It takes significantly stronger magnetic and electric field strengths to move a beam of alpha particles compared with the beam of electrons(betaparticles) because the charge of an alpha particle is twice stronger than a beta particle. Therefore, more energy is needed to move the alpha particle.